In the glorious days, or before the advent of the age of Kali, the women, the children, the old, the cows & spiritual teachers were properly given protection.
1. The protection of women maintains the chastity of society, by which we can get a good generation for peace, tranquility and progress of life.
2. The protection of children gives the human form of life its best chance to prepare the way of liberty from material bondage. Such protection of children begins from the very day of begetting a child by the purificatory process of garbhādhāna-saṁskāra, the beginning of pure life.
3. The protection of the old men gives them a chance to prepare themselves for better life after death.
4. The protection of cows maintains the most miraculous form of food, i.e., milk for maintaining the finer tissues of the brain for understanding higher aims of life.
5. The protection of the learned men (spiritual) maintains the institution of social order and spiritual order, the most scientific culture for attainment of spiritual life.
This complete outlook is based on factors leading to successful humanity as against the civilization of polished cats and dogs. The killing of the above-mentioned innocent creatures is totally forbidden because even by insulting them one loses one’s duration of life. In the age of Kali they are not properly protected, and therefore the duration of life of the present generation has shortened considerably. In the Bhagavad-gītā it is stated that when the women become unchaste for want of proper protection, there are unwanted children called varṇa-saṅkara. To insult a chaste woman means to bring about disaster in the duration of life. Duḥśāsana, a brother of Duryodhana, insulted Draupadī, an ideal chaste lady, and therefore the miscreants died untimely. These are some of the stringent laws of the Lord mentioned above.
Ref >> Srila Prabhupada Vani.